L. Bühler, T. Boeck, V. Chowdhury, D. Krasnov...L. Bühler, T. Boeck, V. Chowdhury, D. Krasnov...

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association www.kit.edu

A3: Magnetically induced instabilities

L. Bühler, T. Boeck, V. Chowdhury, D. Krasnov

LIMTECH-Kick-off meeting, Dresden-Rossendorf 19-20.11.2012

L. Bühler, T. Boeck, V. Chowdhury, D. Krasnov LIMTECH KOM Dresden Rossendorf, 19-20.11.2012

Outline

� Motivation (why MHD at KIT?)

� Experimental setup KIT

� MHD code development and validation KIT

� High-resolution DNS of turbulent flows TUI



Magnetic coils

International Thermonuclear Experimental Reactor

Test blanket

module

(TBM)

Blanket

� Radiation shielding

� Breeding of tritium6Li + n � He + T + energy

� Cooling of the first wall

� Conversion of nuclear power

� Heat removal

Requirements can be accomplished with Li-containing liquids as breeder and coolant

Why MHD at KIT?

⇒⇒⇒⇒ Magnetic confinement of plasma

Liquid metal magnetohydrodynamics (MHD)


Mock-up of a blanket module

Why MHD at KIT?

At KIT in MEKKA we perform ��

Magnet

Manifolds

Pressure pipes

Exit pipe

Inlet pipe

Hartmann wall

Pressure taps

Component tests for ITER liquid metal

blankets using NaK as model fluid



LIMTECH allows complementary basic research which is not covered by fusion program

Goals of A3:

� Investigation of MHD instabilities in liquid metal duct flows

� Study of the influence of magnetic field, flow rate and wall conductance

� Analysis of unstable flow patterns and their nonlinear interactions

� Removing the discrepancy between previous experiments and theory

� Development of reliable computational tools for time-dependent MHD flows

� Application of code to duct flow problems like the planned experiment

� Validation using accurate experiments, extension of existing code capability

� Study of the transition to turbulence and of turbulent transport properties

� Unstable or turbulent MHD flows affect heat and mass transfer in duct flows,

influence performance of liquid metal devices (like fusion blankets)

� Improvement of measuring techniques in liquid metals

� Possibilities for experimental collaboration with other teams in LIMTECH



LIMTECH allows complementary basic research which is not covered by fusion program

� Hartmann layers are linearly stable even for very high Reynolds numbers (Lingwood& Alboussiere 1999, Physics of Fluids) - bypass transition at much lower Reynolds number (Krasnov et al 2004, JFM)

� Jet-like side layers tend to become unstable (inflection points)

� In boundary layers with high velocity jets instabilities develop at relatively low Re

� Linear stability analysis predicts instability of laminar jets for Re > 313 (independently from Ha-number) for a square duct with constant electric wall conductivity (b = 1,

Ting et al. 1991, Int. J. Engng Sci)

� Experiments for MHD flows in electrically conducting ducts show instabilities for� Re > 2650-5300 (b = 1, Reed & Picologlou 1989, Fusion Technology)� Re > 5500-9000 (b = 0.5, Burr et al. 2000, JFM)� Re > 1000 (b = 4, Bühler and Horanyi 2009, Fusion Eng. & Design)

� Numerical simulations (Kinet et al. 2009, Physical Review Letters)

Present knowledge about unstable MHD duct flows


Experiments:

� In side layers high velocity jets are created by Band become unstable

� Test sections with movable probes for velocity

measurements and potential electrodes in walls

Theory:

� Further development of a general finite volume code for investigations of fluid - wall

interactions in strong B fields (KIT)

� Investigations of transition to turbulence and quantification of transport properties

with highly accurate and fast finite difference code (TUI)

Lorentz force density shows unstable flow

y

xz,

B

EM pumpstest section

Turbulence in side layers

(here for insulating walls)

Ha = 350, Re = 105

(TUI)

Cu layer

B

v

z

uy

velocity profile

u (x = 0, y, z)

electrodes in duct walls




Theoretical approaches

� Transition can be studied in the temporal and spatial framework

� Temporal framework: periodic simulation domain, detection of transition

thresholds (simulation is started with laminar state and added noise as initial

condition, Hartmann number/Reynolds number are systematically varied)

� Spatial framework: non-periodic domain as in real experiment, observation of

perturbation amplification in space

� Turbulence simulations typically as temporal simulations

� Very high grid resolutions (>109 grid points) required for the parameter ranges of

interest, very long computational times required for statistical convergence

(only one homogeneous spatial direction for averaging)

� Storage/data handling very demanding for post-processing of simulations

(Terabytes of “snapshot” data)


GaInSn double loop

v

B

electrodes

pump

movable probe

Loop fits completely in the section

of uniform magnetic field

Experiments

� GaInSn as model fluid, loop base materialis electrically insulating

� Two MHD pumps supply the fluid symmetrically to the central test section

� Circuit is positioned in a uniform magneticfield of max 2.1T � no 3D perturbationsas in other experiments at the entranceand exit of magnets



GaInSn double loop

v

B

electrodes

pump

Symmetric entrance flow in test section

movable probe


Loop fits completely in the section

of uniform magnetic field

Experiments

� GaInSn as model fluid, loop base materialis electrically insulating

� Two MHD pumps supply the fluid symmetrically to the central test section

� Circuit is positioned in a uniform magneticfield of max 2.1T � no 3D perturbationsas in other experiments at the entranceand exit of magnets



GaInSn double loop

v

B

electrodes

pump

movable probe

Experiments

potential probes



Movable potential probe

Experiments


First numerical simulation for the GaInSn double loop

Ha = 600

Re = 1100 Bx

z

y

pump

Contours of pressure

test section


L. Bühler, T. Boeck, V. Chowdhury, D. Krasnov...L. Bühler, T. Boeck, V. Chowdhury, D. Krasnov...

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